ON ANASSTHETICS. : 297 
Appendix I. In this connection Mr. Symes has estimated the percent- 
ages of chloroform vapour aspirated from the inner surface of a bottle 
containing a mask upon which were poured equal volumes of (1) chloro- 
form, (2) chloroform and ether mixed, and Dr. Waller has compared the 
relative toxicities on muscle of solutions of chloroform and ether mixture 
and of chloroform alone (Appendix IIT.). 
§ 4. The relative toxicities of chloroform and of ether have been 
systematically estimated by Dr. Waller by a new method and compared 
with that of ethyl alcohol. The method and its results are described 
in a communication to the Royal Society. According to those results 
1 vol. of chloroform is physiologically equivalent to 15 vols. of ether 
(or by weight 1 gramme chloroform=8 grammes ether).* 
Otherwise expressed, the physiological effectiveness of 1 vol. of ether 
is 0067 that of 1 vol. of chloroform, and 1 vol. of chloroform is 
physiologically equivalent to 2°3 vols. of a mixture of 20+3E. 
§ 5. We are agreed that obstruction to respiration, whether by occlu- 
sion of the air passages or by the additional resistance offered to respira- 
tion by apparatus, should be avoided or promptly remedied. We therefore 
deprecate the use of apparatus based on the vacuum principle by which 
the patient aspirates anesthetic vapour by means of a closed mask and 
tube, and consider it essential to any form of apparatus that it should 
be based on the plenum principle, by which an excess of anesthetic 
vapour suftably diluted with air is propelled to an open mask by 
mechanical means sufficient to maintain a slight positive pressure at 
the end of the delivery tube. 
In this connection we think proper to quote two experiments (repre- 
sentative of many others) :— 
§ 6. First Experiment.—The number of respirations per minute 
were taken of a member of the Committee breathing through a closed 
mask and a broad 1-inch tube :— 
A with the end of the tube free. 
B with the tube connected to the outlet of a balance case with the 
inlet connected to a force pump, working at between 10 and 15 litres per 
minute, giving at the mask a positive air-pressure equal to between 1 and 
2 millimetres of water. 
The normal respiration-frequency of the subject was 16 per minute. 
The frequency under the conditions A quickly became 20, rose to 40, 
and culminated in dyspnoea, so that the mask had to be removed. 
The frequency under the condition of B fell to 10 and 9, and the 
subject breathed from the closed mask for an indefinite time without 
feeling any inconvenience. 
These results, in our opinion, sufficiently illustrate the ease with 
which dyspncea can be produced in the human subject by slight obstruc- 
tion and the contrary effect of air-supply delivered under positive 
pressure. 
§ 7. The second experiment, on a cat, was made in order to see 
whether the toxic effects of chloroform were aggravated by obstructed 
respiration. The result was not in accordance with our expectation: no 
appreciable aggravation of toxic effect was caused by very considerable 
+ Since this report was adopted Waller and Symes, by a different method, have 
arrived at the same result, yiz., 1 gramme chloroform = 8 grammes ether (see 
Appendix VI.). 
